The prior art makes available a number of OLEDs emitting red and/or green light. OLEDs that radiate deep blue, light blue and/or blue-green and having acceptable, i.e. economically more attractive, life spans are less common.
Cotton et al. showed that the hpp ligand (anion of 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]primidine=Hhpp) has the extraordinary ability of stabilizing complexes in high oxidation states because of its enormous basicity (F. A. Cotton, L. M. Daniels, C. A. Murillo, D. J. Timmons, C. C. Wilkinson, J. Am. Chem. Soc. 2002, 124, 9249-9256, and Tab. 3 from F. A. Cotton, N. E. Gruhn, J. Gu, P. Huang, D. L. Lichtenberger, C. A. Murillo, L. O. van Dorn, C. C. Wilkinson; “Closed-Shell Molecules That Ionize More Readily Than Cesium,” Science Vol 298 (2002) 1971.).